A known injection molding machine disclosed in German Pat. No. 1 136 819, for non-metal plastic materials, in particular thermoplastic and thermosetting plastic, has an injection unit having an injection cylinder and an incrementally indexable turntable supporting a plurality of molds. The plane of the table is parallel to the injection cylinder axis, and the arrangement is such that the injection cylinder and the turntable are supported so that either one of the two parts is displaceable relative to the other, or both parts are displaceable toward or away from one another in the direction of the plane of the table. The particular mold located in an operating position at a given time, when contacting the injection nozzle of the injection cylinder, acts directly in the valve opening direction upon a valve that closes the injection nozzle.
Since in this machine the individual molds always remain with both mold halves on the turntable, each of the molds has to have its own associated mold closing mechanism, which is located on the turntable. This is expensive, and it is problematic in terms of the space required for it. Furthermore, the injection nozzle of the injection unit must be aligned exactly with the feed supply, or sprue opening of the mold to be filled; this means that the turntable and the injection unit must have highly accurate mutual guidance. In practical terms, this can be achieved only by locating the carriage that supports the turntable and the injection unit on a common frame or support, which has suitable precision guide means. In principle, therefore, such an injection molding machine has only a single mold turntable, which is associated with the injection unit and cannot be operationally disassociated from the injection unit. Accordingly, a mold exchange must be done on the turntable itself, which necessitates shutting down the entire injection molding machine.
This kind of interruption in operation caused by a mold change is a hindrance to fully continuous, 24-hour operation of the injection molding machine, especially whenever relatively small quantities of different molded articles are to be produced in succession. Each interruption of a continuous injection molding process moreover unavoidably produces increased rejects and scrap.